1. Field of the Invention
The present invention relates to an oscillating inner gearing planetary gear system and a geared motor having the same.
2. Description of the Related Art
An oscillating inner gearing planetary gear system has an external gear and internal gears which have a slight difference in the number of teeth with the external gear. Rotation speed of an input shaft is reduced by one of either the external gear or the internal gears oscillating with respect to the other, and the speed-reduced output is delivered by an output shaft. This type of system is found in various areas in which reducers are used, owing to the advantages of large torque transmission being possible and large reduction ratios being obtainable.
For example, Japanese Patent No. 2607937 discloses an internal oscillating inner gearing planetary gear system in which rotation of an input shaft is reduced and delivered by an output member through oscillatingly rotating internal gears around an external gear. The internal gear has a slight difference in the number of teeth with the external gear.
An example of the same gear system will now be explained with reference to FIGS. 6 and 7.
In the FIGS. 6 and 7, a casing 1 has a first support block 1A and a second support block 1B joined together by insertion of an engaging member such as bolts or pins (omitted in drawings) into engaging holes 2. A pinion 6 is disposed on the end of an input shaft 5. The pinion 6 meshes with a plurality of transmitting gears 7 disposed at equal angles around the input shaft 5.
Three eccentric shafts 10 are disposed in the casing 1 at equal-angled intervals (120 degree intervals) circumferentially. The eccentric shafts 10 are supported to be freely rotatable by bearings 8 and 9 at both axial ends and have eccentric bodies 10A and 10B which are in an axially midway portion thereof. The transmitting gears 7 are joined to respective end portions of the eccentric shafts 10. The transmitting gears 7 are rotated by the rotation of the input shaft 5, to rotate each of the eccentric shafts 10.
The eccentric shafts 10 pass through eccentric holes 11A and 11B of two internal oscillating bodies 12A and 12B contained in the casing 1, respectively. Rollers 14A and 14B are disposed between outer circumferences of the two eccentric bodies 10A and 10B adjoined in the axial direction of the eccentric shafts 10 and inner circumferences of the through-holes of the internal oscillating bodies 12A and 12B, respectively.
An external gear 21 integrated with the end of an output shaft 20 is disposed at the central portion inside the casing 1. Internal teeth 13 formed from pins of the internal oscillating bodies 12A and 12B mesh with external teeth 23 of the external gear 21. A difference in the number of teeth between the external teeth 23 of the external gear 21 and the internal teeth 13 of the internal oscillating bodies 12A and 12B is set to be slight (for example, in a range of about 1 to 4).
The gear system operates in the following manner. Rotation of the input shaft 5 is delivered to the transmitting gears 7 through the pinion 6. The eccentric shafts 10 are then rotated by the transmitting gears 7. The eccentric bodies 10A and 10B rotate due to rotation of the eccentric shafts 10, then, the internal oscillating bodies 12A and 12B oscillatingly rotate due to the rotation of the eccentric bodies 10A and 10B. With this arrangement, through one rotation of the oscillating rotation of the internal oscillating bodies 12A and 12B, a phase of the external gear 21 which meshes with the internal oscillating bodies 12A and 12B is shifted by the difference in the number of teeth. Thus, a rotation component equivalent to the phase difference becomes the (reduction) rotation of the external gear 21, and speed-reduced output is delivered from the output shaft 20.
Moreover, as this kind of oscillating inner gearing planetary gear systems, in addition to the discussed internal teeth oscillating type in which internal oscillating bodies are oscillated, external teeth oscillating types in which an external gear is oscillated are also known and widely used.
Among the types wherein an external gear is oscillated, there are types where an eccentric body for oscillatingly rotating the external gear is disposed at the outer circumference of an input shaft (coaxially with the input shaft axle), as well as types where a plurality of eccentric shafts are provided passing through an external gear, rotation of the input shaft is distributed and transmitted to the plurality of eccentric shafts, and all eccentric shafts are rotated in phase (for example, U.S. Pat. No. 4,846,018).
However, in these known gear systems, when a driving source (such as a motor) is connected to the input shaft, a large space (space to accommodate the system) is occupied both radially and axially, given that the axial direction length is long since an input shaft is located coaxially with an output shaft, and the gear system itself has a considerable radial dimension to begin with. As a result, installation to a partnered apparatus (driven apparatus) was sometimes difficult depending on the application, installation conditions, or other aspects. There was also a problem that a large volume is required per single unit when storing as stock or transporting in the form of a geared motor.
Also, when attempts were made at a design having a hollow shaft passing through the entire gear system, a construction where the axis of a driving source is offset from the axis of the input shaft (by insertion of an idler gear or similar means) came to be employed, since it was difficult to design a driving source such as a motor connected with the input shaft, with a through-hole as well. However, with this arrangement, a new problem arose of the axial length becoming even longer, since it is necessary to insert an idler gear for offsetting the axis.
Even if a hollow shaft were to be adopted, it would mean forming a space inside an input shaft rotating at high speed, and thus, for example, to locate wire harnesses, cooling water piping, etc. in the space, it would be necessary to install protective piping which would be held so as not to rotate by separate bearings disposed between the protective piping itself and the inner circumference of the input shaft. In this respect as well problems arose of difficulty in maintaining a large enough space, as well as an increase in cost.